Method for the fractional condensation of a hot gas mixture containing acrylic acid or methacrylic acid and having a high proportion of non-condensable constituents

Abstract

A process for the fractional condensation of a gas mixture which, in addition to acrylic acid or methacrylic acid, also contains at least one further condensable component and additionally a high proportion of one or more noncondensable components, wherein the gas mixture is passed through a column having separatory internals and the condensable components are condensed by cooling.

We claim:  
     
       1. A process for the fractional condensation of a gas mixture comprising acrylic acid or methacrylic acid, at least one further condensable component, and additionally a high proportion of one or more noncondensable components, the process comprising passing the gas mixture through a column having separatory internals, condensing the condensable components by cooling, and removing acrylic acid or methacrylic acid having a purity of more than 95% by weight from the column. 
     
     
       2. The process as claimed in  claim 1 , wherein the gas mixture is a crude product formed by catalytic gas-phase oxidation of C 3 -/C 4 -alkanes, -alkenes, -alkanols and/or -alkanals and/or at least one intermediate thereof selected from the group consisting of isobutyric acid and methyl tert-butyl ether to give acrylic acid or methacrylic acid. 
     
     
       3. The process as claimed in  claim 1 , wherein the gas mixture is cooled before the condensation. 
     
     
       4. The process as claimed in  claim 1 , wherein the gas mixture is a hot gas mixture having a high boiler fraction comprising one or more compounds selected from the group consisting of maleic anhydride, benzoic acid, stabilizers, monomeric and oligomeric acrylic acid, a medium boiler fraction comprising acrylic or methacrylic acid, and a low boiler fraction comprising one or more compounds selected from the group consisting of water, acetic acid, and formaldehyde, and the hot gas mixture is condensed. 
     
     
       5. A process as claimed in  claim 4 , wherein each of the high boiler, medium boiler and low boiler fractions contains one or more components. 
     
     
       6. The process as claimed in  claim 1 , wherein the gas mixture is a hot gas mixture comprising from 20 to 98% by weight of noncondensable components selected from the group consisting of nitrogen, oxygen, carbon monoxide, methane, propane, and propene, based on 100% by weight of the gas mixture, and the hot gas mixture is condensed. 
     
     
       7. The process as claimed in  claim 1 , wherein the gas mixture is a hot gas mixture at from 100 to 350° C., and the hot gas mixture is condensed. 
     
     
       8. The process as claimed in  claim 1 , wherein a column having one or more cooling apparatuses is used. 
     
     
       9. The process as claimed in  claim 1 , wherein the separatory column internals are selected from the group consisting of stacked packings, dumped packings, trays, and combinations thereof. 
     
     
       10. A process for the preparation of acrylic acid or methacrylic acid by catalytic gas-phase oxidation of a starting material comprising at least one compound selected from the group consisting of C 3 -/C 4 -alkanes, -alkenes, -alkanols and/or -alkanals and/or at least one intermediate thereof selected from the group consisting of isobutyric acid and methyl tert-butyl ether with formation of a gaseous crude product comprising acrylic acid or methacrylic acid, at least one byproduct selected from the group consisting of acrolein, methacrolein, propene, isobutene, steam, carbon monoxide, carbon dioxide, nitrogen, oxygen, acetic acid, propionic acid, formaldehyde, aldehydes other than formaldehyde, and maleic anhydride, and/or at least one unconverted starting material, wherein the gaseous crude product is condensed by a process as claimed in  claim 1 . 
     
     
       11. The process as claimed in  claim 1 , wherein the gas mixture is cooled to 50 to 300° C. 
     
     
       12. The process as claimed in  claim 1 , wherein the gas mixture is cooled to 70 to 200° C. 
     
     
       13. The process as claimed in  claim 1 , wherein the gas mixture comprises 1 to 30% by weight of acrylic acid or methacrylic acid, and 0.05 to 1% by weight acrolein or methacrolein. 
     
     
       14. A process for the purification of acrylic or methacrylic acid comprising: 
       cooling a hot gas mixture comprising acrylic or methacrylic acid, at least one additional condensable component selected from the group consisting of water, acetic acid, formaldehyde, maleic anhydride, benzoic acid, acrolein, phthalic anhydride, propionic acid, maleic acid, allyl acrylate, benzaldehyde, fufural, and phenothiazine, and 20-98% by weight of a noncondensable component selected from the group consisting of nitrogen, oxygen, carbon monoxide, carbon dioxide, methane, propane and propene;  
       injecting the cooled gas into a column comprising separatory internals at a lower portion of the column;  
       removing the heat of condensation from the lower portion of the column with a heat exchanger, thereby removing a condensed high boiler fraction comprising one or more compounds selected from the group consisting of maleic anhydride, benzoic acid, stabilizers, monomeric and oligomeric acrylic acid from the column;  
       recirculating a portion of the condensed high boiler fraction into the column;  
       removing a medium boiler fraction comprising acrylic acid or methacrylic acid at a middle portion of the column;  
       removing the heat of condensation from an upper portion of the column with a heat exchanger, thereby removing a condensed low boiler fraction comprising one or more compounds selected from the group consisting of water, acetic acid, and formaldehyde from the column;  
       recirculating a portion of the condensed low boiler fraction into the column;  
       removing uncondensed gases from the upper portion of the column.